Implantable cardiac stimulation devices are well known in the art. Such devices may include, for example, implantable cardiac pacemakers and defibrillators. The devices are generally implanted in a pectoral region of the chest beneath the skin of a patient within what is known as a subcutaneous pocket. The implantable devices generally function in association with one or more electrode carrying leads which are implanted within the heart. The electrodes are usually positioned within the right side of the heart, either within the right ventricle or right atrium, or both, for making electrical contact with their respective heart chamber. Conductors within the leads couple the electrodes to the device to enable the device to sense cardiac electrical activity and deliver the desired therapy.
Traditionally, therapy delivery had been limited to the venous, or right side of the heart. The reason for this is that implanted electrodes can cause blood clot formation in some patients. If a blood clot were released arterially from the heart left side, as for example the left ventricle, it could pass directly to the brain potentially resulting in a paralyzing or fatal stroke. However, a blood clot released from the right heart, as from the right ventricle, would pass into the lungs where the filtering action of the lungs would prevent a fatal or debilitating embolism in the brain.
Recently, new lead structures and methods have been proposed and even practiced for delivering cardiac rhythm management therapy to the left heart. These lead structures and methods avoid direct electrode placement within the left atrium and left ventricle of the heart by lead implantation within the coronary sinus region of the heart. As used herein, the phrase “coronary sinus region” refers to the venous vasculature of the left ventricle, including any portions of the coronary sinus, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus.
It has been demonstrated that electrodes placed in the coronary sinus region of the heart may be used for left atrial pacing, left ventricular pacing, and cardioversion and defibrillation. These advancements enable implantable cardiac stimulation devices to address the needs of a patient population with left ventricular dysfunction and/or congestive heart failure which would benefit from left heart side pacing, either alone or in conjunction with right heart side pacing (bi-chamber pacing), and/or defibrillation. Many present CHF devices require both a lead in the left ventricle (LV) and a separate lead in the right ventricle (RV), the RV lead intended for pacing the right ventricular apex or tip of the right ventricle while the LV lead is for pacing the left ventricle to obtain better synchronization together which results in improved hemodynamics. The significance of a single lead for positioning only in the left ventricle is that it is easier and less time consuming to install only one lead rather than two and, additionally two leads can “saw” against each other where they cross in the RA (right atrium), potentially resulting in damage to their insulation.
By pacing simultaneously from the distal, apical electrode to the more proximal, basal electrode ring in the LV, a more efficient contraction is obtained, with improved cardiac output, and patients are found to have more energy. In this regard, it should be noted that the “simultaneous” stimulation is often better achieved when there is a time separation of up to 50 ms between the two sites.
Cardiac leads intended for use in providing both cardiac pacing and defibrillation in the left heart via the coronary sinus region have previously been difficult to position due to the tortuous venous routes of the human anatomy. Moreover, to provide both pacing and defibrillation of both the left atrium and the left ventricle from the coronary sinus region with multiple leads employing the appropriate types of electrodes is extremely difficult given the space constraints to accommodate multiple leads in the coronary sinus region. Hence, such known implants have been too cumbersome, difficult, and time consuming to perform and likely resulted in compromised performance or system malfunction.
Typical of known implantable cardiac leads for use in the coronary sinus region of the heart are U.S. Pat. Nos. 6,295,475 to Morgan entitled “Single-Pass Atrial Ventricular Lead with Multiple Atrial Ring Electrodes and a Selective Atrial Electrode Adapter for the Coronary Sinus Region”, U.S. Pat. No. 6,490,489 to Bornzin et al. entitled “Implantable Cardiac Single Pass Coronary Sinus Lead for Providing Pacing and Defibrillation and Method of Manufacture”, and 6,650,945 to Helland et al. entitled “Implantable Cardiac Coronary Sinus Lead Having a Defibrillation Electrode of Split Configuration and Method of Manufacture”, as well as U.S. Publication No. US 2002/0103524 to Bornzin et al. entitled “Implantable Cardiac Single Pass Coronary Sinus Lead for Providing Pacing and Defibrillation and Method of Manufacture”.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.